textproduct: Quad Cities

KEY MESSAGES

- Heat and humidity builds into the area for much of the work week with heat indices of 95 to potentially over 100. Heat Advisories have been issued for most areas along/south of I-80. Tuesday and Wednesday look to be the hottest days of the week.

- The Storm Prediction Center has a Marginal, level 1 out of 5, Risk for severe storms today and Tuesday for areas along/north of Highway 30. Damaging winds are the primary risk with hail a secondary risk.

- Weak upper level disturbances bring a near daily risk of showers and storms, mainly for areas north of I-80.

SHORT TERM /THROUGH TONIGHT/

Issued at 230 AM CDT Mon Aug 31 2026

The heat dome builds into the area today while a slightly weaker LLJ continues to transport moisture into the area. At the same time negative theta e values with relatively steep mid-level lapse rates should allow weak nocturnal showers to develop prior to sunrise mainly along/east of the Mississippi. A rogue rumble of thunder cannot be ruled out. The nocturnal convection that develops will dissipate by late morning as the LLJ weakens.

A subtle upper air disturbance moving east from the Plains will combine with daytime heating to generate isolated diurnal convection. REFS shows this scenario with any convection dissipating around sunset. Given favorable mid-level lapse rates, an isolated severe storm cannot be ruled out. Thus the Marginal, level 1 out of 5, Risk for areas along/north of Highway 30 looks reasonable. Hail and damaging winds would be the primary risks.

The question today is how warm will it get. NBM has been way too warm as of late and temperatures have been adjusting downward to reflect this and the potential for more clouds.

The corn has begun to fire thus we are past the peak transpiration period so dew points much above 73 would be isolated with upper 60s to lower 70s more common. For today this should result in peak afternoon heat indices of 95 to 100.

Tonight has a lot of questions. Going on the premise the NBM is too warm, the active nocturnal storm track would be closer to the area; potentially across the northern half. Given the weak forcing, the very short term models are not developing much in the way of nocturnal convection. However, internally, several models are giving subtle signals for a small cluster of storms. Again, going on the premise the NBM is too warm, this nocturnal convection could impact areas north of Highway 30. Right now will only increase rain chances to 20% for this area with the idea of watching trends to see if pops need to be increased further.

The potential is there for record warm lows to be challenged this week. Refer to the climate section for more information.

LONG TERM /TUESDAY THROUGH SUNDAY/

Issued at 219 PM CDT Sun Aug 30 2026

Tuesday will need to be watched for the potential of isolated strong to severe storms over the northern portions of our region as additional shortwave impulses ride the top of the heat dome. This severe storms risk appears to be conditional, and thus, confidence is low for storms to become severe. However, given sufficient MUCAPE values around 2000-3000 J/kg, combined with 25 to 35 knots of 0-6 km shear, the convective parameter space would be supportive of strong/severe storms late Monday night and again Tuesday afternoon if anything develops. Overall, the large scale forcing from these shortwaves remains pretty weak, so SPC continues to have only a Marginal Risk (level 1 of 5) for severe storms for these time frames. The Tuesday afternoon storm potential will have the potential to limit daytime heating, and thus, limiting the heat indices. Storms will be most likely north of I-80 for each time frame.

Outside of the storm threat, we will continue to have hot and humid conditions over at least the southern portions of the area where storm chances are much more limited through much of the week. Confidence in the hot conditions Tuesday through Thursday remain high, given the latest ECMWF EFI/Shift of Tails values for high temperatures Tuesday through Thursday are in excess of 0.8 to 0.9 (even some values over 0.95 in isolated spots), along with Shift of Tails values around 1. This suggests high confidence in anomalously warm high temperatures, although not extreme values based on the lower Shift of Tails. With the potential for these anomalously hot conditions to last this week, we've decided to have the Heat Advisory go through the daylight hours Wednesday. It's entirely possible for the advisory to be extended into Thursday, given LREF ensemble exceedance probabilities of 100 degree heat indices approaching 50% across our southern two tiers of counties. Additionally, overnight lows might not dip below 75 degrees Monday night through Wednesday night, so this would compound the heat stress - even at night. There is potential for some record warm low temperatures during this period. See the Climate section below for the current records.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 1211 AM CDT Mon Aug 31 2026

LLWS in the 1-1.5 kft AGL layer will again be seen through sunrise as a 40-45 knot LLJ will be over the area. Weak signals suggest the potential for 15-30% coverage of SHRA and maybe some TSRA east of the Mississippi River toward sunrise. Another round but potentially more isolated SHRA/TSRA is possible north of Highway 30 during the afternoon. Density altitudes of 2-3 kft are possible during the afternoon hours.

CLIMATE

Issued at 222 PM CDT Sun Aug 30 2026

Record Warm Low Temperatures:

August 30: KMLI: 75/1947

August 31: KDBQ: 74/2000 KMLI: 75/2000

September 1: KDBQ: 73/1937 KMLI: 75/1913

September 2: KDBQ: 74/2011 KMLI: 77/1913

September 3: KDBQ: 73/1939 KMLI: 76/1939

September 4: KDBQ: 71/1912 KMLI: 74/2018

DVN WATCHES/WARNINGS/ADVISORIES

IA...Heat Advisory from 1 PM this afternoon to 7 PM CDT Wednesday for IAZ063>065-067-068-076>078-087>089-098-099. IL...Heat Advisory from 1 PM this afternoon to 7 PM CDT Wednesday for ILZ015-016-024>026-034-035. MO...Heat Advisory from 1 PM this afternoon to 7 PM CDT Wednesday for MOZ009-010.